(Perfusion Lung Scan, Lung Perfusion Scintigraphy, Radionuclide Pulmonary Scan, Ventilation-Perfusion Scan, V/Q Scan)

Procedure Overview

What is a lung scan?

A lung scan is a specialized radiology procedure used to examine the lungs to identify certain conditions. A lung scan may also be used to follow the progress of treatment of certain conditions.

A lung scan is a type of nuclear radiology procedure. This means that a tiny amount of a radioactive substance is used during the procedure to assist in the examination of the lungs.

There are two types of lung scans: ventilation scans and perfusion scans. A ventilation scan evaluates ventilation, or the movement of air into and out of the bronchi and bronchioles. A perfusion scan evaluates blood flow within the lungs. In the case of suspected pulmonary embolus, both ventilation and perfusion scans are performed either simultaneously or one immediately after the other. If ventilation is normal but perfusion is abnormal, a "mismatch" is said to exist. This mismatch is often indicative of a pulmonary embolus.

The radioactive substance, called a radionuclide (radiopharmaceutical or radioactive tracer), will collect at spots of abnormal blood flow in a perfusion scan. In a ventilation scan, the radionuclide will fill the lungs unless there is an area through which air cannot move. The radiation emitted by the radionuclide is detected by a scanner, which processes the information into a picture of the lungs. Areas in which the radionuclide collects are referred to as "hot spots," while areas of minimal or no collection of radionuclide are called "cold spots."

Lung scans are most often used to diagnose and locate emboli (clots or other small tissue masses) within the blood vessels of the lungs. However, other conditions of the lungs may be evaluated with a lung scan.

Other related procedures that may be used to diagnose problems of the lungs and respiratory tract include bronchoscopy, computed tomography (CT scan) of the chest, chest fluoroscopy, chest x-ray, chest ultrasound, lung biopsy, bronchography, mediastinoscopy, oximetry, peak flow measurement, positron emission tomography (PET) scan, pleural biopsy, pulmonary angiography, pulmonary function tests, and thoracentesis. Please see these procedures for additional information.

Anatomy of the respiratory system

The respiratory system is made up of the organs involved in the interchanges of gases, and consists of the:

  • Nose

  • Pharynx

  • Larynx

  • Trachea

  • Bronchi

  • Lungs

The upper respiratory tract includes the:

  • Nose

  • Nasal cavity

  • Ethmoidal air cells

  • Frontal sinuses

  • Maxillary sinus

  • Larynx

  • Trachea

The lower respiratory tract includes the lungs, bronchi, and alveoli.

What are the functions of the lungs?

The lungs take in oxygen, which cells need to live and carry out their normal functions. The lungs also get rid of carbon dioxide, a waste product of the body's cells.

The lungs are a pair of cone-shaped organs made up of spongy, pinkish-gray tissue. They take up most of the space in the chest, or the thorax (the part of the body between the base of the neck and diaphragm).

The lungs are enveloped in a membrane called the pleura.

The lungs are separated from each other by the mediastinum, an area that contains the following:

  • The heart and its large vessels

  • Trachea (windpipe)

  • Esophagus

  • Thymus

  • Lymph nodes

The right lung has three sections, called lobes. The left lung has two lobes. When you breathe, the air enters the body through the nose or the mouth. It then travels down the throat through the larynx (voice box) and trachea (windpipe) and goes into the lungs through tubes called main-stem bronchi.

One main-stem bronchus leads to the right lung and one to the left lung. In the lungs, the main-stem bronchi divide into smaller bronchi and then into even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli.

Reasons for the Procedure

A lung scan is most often performed when symptoms such as tachycardia (fast heart rate), dyspnea (difficulty in breathing), decreased oxygen saturation, chest pain not related to the heart, and other symptoms suggest the presence of a pulmonary embolus.

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